On Fri, Oct 16, 2009 at 07:38:24PM +0800, Wu Zhangjin wrote:>trace_clock_local() is based on the arch-specific sched_clock(), in X86,>it is tsc(64bit) based, which can give very high precision(about 1ns>with 1GHz). but in MIPS, the sched_clock() is jiffies based, which can>give only 10ms precison with 1000 HZ. which is not enough for tracing,>especially for Real Time system.>>so, we need to implement a MIPS specific sched_clock() to get higher>precision. There is a tsc like clock counter register in MIPS, whose>frequency is half of the processor, so, if the cpu frequency is 800MHz,>the time precision reaches 2.5ns, which is very good for tracing, even>for Real Time system.>>but 'Cause it is only 32bit long, which will rollover quickly, so, such>a sched_clock() will bring with extra load, which is not good for the>whole system. so, we only need to implement a arch-specific>trace_clock_local() for tracing. as a preparation, we convert it as a>weak function.>>The MIPS specific trace_clock_local() is coming in the next patch.>>Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>>---> kernel/trace/trace_clock.c | 2 +-> 1 files changed, 1 insertions(+), 1 deletions(-)>>diff --git a/kernel/trace/trace_clock.c b/kernel/trace/trace_clock.c>index 20c5f92..a04dc18 100644>--- a/kernel/trace/trace_clock.c>+++ b/kernel/trace/trace_clock.c>@@ -26,7 +26,7 @@> * Useful for tracing that does not cross to other CPUs nor> * does it go through idle events.> */>-u64 notrace trace_clock_local(void)>+u64 __attribute__((weak)) notrace trace_clock_local(void)